neat find

From: Tony Duell <ard(a)p850ug1.demon.co.uk> To: Discussion re-collecting of classic computers

Subject: Re: neat find Date: Tuesday, April 14, 1998 3:14 PM > > today at goodwill I found a Advance Micro Device AM2900 Evaluation & > Learning Kit in the it's box (very nice design on it) with one

The comment 'you lucky beggar' springs to mind !. The AMD 2900 series of chips were essentially a build-it-yourself CPU. The main ones were : The 2901 - a 4 bit ALU + registers. You could cascade these to give you

many bits as you wanted (in multiples of 4). There was also a fast carry generator, equivalent to the 74182. Was that the 2902? The 2903 was an enchanced 2901 AFAIK. I never used it. Then there were the 2909 and 2911 4-bit microcode sequencers. You cascaded those as well to access whatever size control store you wanted. Add a bit of jump logic, and write the microcode to control your CPU. For simpler designes there was the 2910 12 bit sequencer which couldn't easily be extended (*). That would seqeunce a 4K control store, and had some of the jump control logic built-in. I've done a bit with these chips, and was reading the data books earlier today, actually. Great pity they're no longer made... (*) PERQ systems used a 2910 as the sequencer on the 4K PERQ CPU board. The 16K CPU board also used a 2910 with a '2 bit kludge' to provide the extra address lines. The pun on '2 bit' is intentional, and will be understood by anybody who's ever written PERQ microcode... -tony